U.S. patent application number 09/122852 was filed with the patent office on 2002-01-03 for projection display.
Invention is credited to HATANAKA, MASATO, KATSURAGAWA, HIDEKI, TAGAWA, YUSAKU.
Application Number | 20020001131 09/122852 |
Document ID | / |
Family ID | 16474819 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020001131 |
Kind Code |
A1 |
HATANAKA, MASATO ; et
al. |
January 3, 2002 |
PROJECTION DISPLAY
Abstract
Disclosed is a projection display for projecting an image
displayed on an image display element on a screen using light rays
generated by a light source, wherein sheet-type polarized light
separating mirrors each having a plane tilted at an angle of 10 to
30.degree. with respect to an optical axis of the light source are
disposed between the image display element and the light source,
whereby the projection display can be miniaturized with the reduced
cost.
Inventors: |
HATANAKA, MASATO; (SAITAMA,
JP) ; TAGAWA, YUSAKU; (TOKYO, JP) ;
KATSURAGAWA, HIDEKI; (TOKYO, JP) |
Correspondence
Address: |
JAY H MAIOLI
COOPER & DUNHAM
1185 AVENUE OF THE AMERICAS
NEW YORK
NY
10036
|
Family ID: |
16474819 |
Appl. No.: |
09/122852 |
Filed: |
July 28, 1998 |
Current U.S.
Class: |
359/485.07 ;
348/E5.143; 348/E9.027 |
Current CPC
Class: |
G02B 27/286 20130101;
H04N 9/3105 20130101; H04N 9/3141 20130101; H04N 9/3144 20130101;
H04N 9/3167 20130101 |
Class at
Publication: |
359/485 |
International
Class: |
G02B 005/30; G02B
027/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 29, 1997 |
JP |
P09-203478 |
Claims
What is claimed is:
1. A projection display for projecting an image displayed on an
image display element on a screen using light rays generated by a
light source, comprising: a sheet-type polarized light separating
mirror with its plane tilted at an angle of 10 to 30.degree. with
respect to an optical axis of said light source, said mirror being
disposed between said image display element and said light source
for separating a first polarized light component and a second
polarized light component from each other, and converting either
the first polarized light component or the second polarized light
component, thereby unifying both the polarized light components
into either the first polarized light component or the second
polarized light component.
2. A projection display according to claim 1, wherein said
sheet-type polarized light separating mirror is coated with a
single TiO.sub.2 film.
3. A projection display according to claim 1, wherein said light
source generates substantially parallel light rays, and said
polarized light separating mirror is disposed between said light
source and an optical integrator.
4. A projection display according to claim 1, wherein said
sheet-type polarized light separating mirror is composed of a first
sheet-type polarized light separating mirror and a second
sheet-type polarized light separating mirror, said first and second
sheet-type polarized light separating mirrors being disposed
symmetrically with respect to the optical axis of said light
source.
5. A projection display according to claim 1, wherein said image
display element is a liquid crystal display.
6. A projection display according to claim 1, wherein the image
displayed on said image display element is reflected from a mirror
and is then projected on a backface of the screen.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an improved projection
display for projecting an image displayed on an image display
element on a screen using light rays generated by a light
source.
[0002] A so-called projection display for projecting an image
displayed on an image display element on a screen using light rays
generated by a light source is disclosed, for example, in Japanese
Patent Laid-open Nos. Hei 2-253247 and Hei 5-19209. The projection
display disclosed in the former document employs a prism type
polarizer, and the projection display disclosed in the latter
document employs a polarizer composed of a plurality of glass
sheets each having a Brewster angle. The prism type polarizer and
the polarizer making use of the Brewster angle are adapted to
remove a light component to be absorbed in the projection display
and hence to reduce a heat load which is imparted to an optical
system from light rays generated by a light source; and to increase
an optical efficiency of a necessary polarized wave by
polarization-conversion of an unnecessary polarized wave.
[0003] The projection display using the prism type polarizer
disclosed in the former document, however, has a problem that the
prism type polarizer has a large-size and is expensive. Meanwhile,
the projection display using the glass sheets disclosed in the
latter document, however, has a problem that the separation
characteristic is physically limited depending on the Brewster
angle and is not necessarily desirable, and therefore, a desirable
characteristic must be attained by use of a plurality of glass
sheets.
SUMMARY OF THE INVENTION
[0004] An object of the present invention is to provide a
projection display which can be miniaturized with the reduced
cost.
[0005] To achieve the above object, according to the present
invention, there is provided a projection display for projecting an
image displayed on an image display element on a screen using light
rays generated by a light source, including: a sheet-type polarized
light separating mirror with its plane tilted at an angle of 10 to
30.degree. with respect to an optical axis of the light source, the
mirror being disposed between the image display element and the
light source for separating a first polarized light component and a
second polarized light component from each other, and converting
either the first polarized light component or the second polarized
light component, thereby unifying both the polarized light
components into either the first polarized light component or the
second polarized light component.
[0006] According to the present invention, in the projection
display for projecting an image displayed on the image display
element on a screen using light rays generated by a light source,
the sheet-type polarized light separating mirror with its plane
tilted at an angle of 10 to 30.degree. with respect to the optical
axis of the light source is disposed between the image display
element and the light source. Accordingly, the sheet-type polarized
light separating mirror is capable of removing a light component to
be absorbed in the projection display, thereby reducing a heat load
which is applied to the optical system from the light rays
generated by the light source. The sheet-type polarized light
separating mirror can be prepared at a cost lower than that of the
prism type polarizer, and can be miniaturized because the plane
thereof is tilted at a relatively small angle of 10 to 30.degree.
with respect to the optical axis of the light source.
[0007] If the tilting angle of the plane is less than 10.degree. or
more than 30.degree., it is difficult to sufficiently separate the
first and second polarized light components from each other.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a perspective view of a television set as a
preferred embodiment to which a projection display of the present
invention is applied;
[0009] FIG. 2 is a sectional view of the television set, taken on
line A-A of FIG. 1;
[0010] FIG. 3 is a perspective view showing a preferred embodiment
of the projection display of the present invention shown in FIG.
2;
[0011] FIG. 4 is a plan view showing the projection display seen
from the direction shown by an arrow A1 of FIG. 3;
[0012] FIG. 5 is a view showing the internal structure of the
projection display shown in FIG. 4;
[0013] FIG. 6 is a schematic view showing only an optical system of
the projection display shown in FIG. 5;
[0014] FIG. 7 is a perspective view showing one example of a PS
conversion unit shown in FIGS. 5 and 6;
[0015] FIG. 8 is a view showing a positional relationship between
the optical system of the PS conversion unit shown in FIG. 7 and
the light source;
[0016] FIG. 9 is a view showing a positional relationship between
the polarized light separating mirror and the light source;
[0017] FIG. 10 is a diagram showing one example of the separation
characteristic of the polarized light separating mirror;
[0018] FIG. 11 is a view showing one example of a first fly eye
lens;
[0019] FIG. 12 is a view showing one example of a second fly eye
lens;
[0020] FIG. 13 is a view showing another example of the second fly
eye lens;
[0021] FIG. 14 is a view showing another embodiment of the
projection display of the present invention;
[0022] FIG. 15 is a view showing a further embodiment of the
projection display of the present invention;
[0023] FIG. 16 is a view showing a further embodiment of the
projection display of the present invention; and
[0024] FIG. 17 is a view showing a further embodiment of the
projection display of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Hereinafter, preferred embodiments of the present invention
will be described with reference to the accompanying drawings.
[0026] It is to be noted that although the following embodiments
will be described using specific terms, such description is
illustrative purposes only, and it is to be understood that the
scope of the present invention is not limited to the embodiments
unless otherwise specified in terms of the limitation of the
present invention.
[0027] FIG. 1 is a view showing the external appearance of a
preferred embodiment in which a projection display 1 of the present
invention is applied, and FIG. 2 is a sectional view, taken on line
A-A of FIG. 1, showing the internal structure of a backface
projection television set 100 of a liquid crystal type including
the projection display 1 shown in FIG. 1.
[0028] A schematic structure of the television set 100 will be
first described. Referring to FIGS. 1 and 2, the television set 100
houses a cabinet 101, a screen 102, a mirror 103 and the projection
display 1. Light rays 5 to be projected, which are formed from
light rays of a light source 3, go out of the projection display 1,
being reflected from the mirror 103, and are projected to a
backface 104 of the screen 102. It is to be noted that in the
following description the term "projection" is equivalent to a term
"incidence".
[0029] An image projected on the screen 102 can be viewed by a user
U as a black-and-white image or a color image.
[0030] In the description of the following embodiments it is
assumed that a color image is displayed on the screen 102.
[0031] A preferred embodiment of the projection display 1 shown in
FIGS. 1 and 2 will be described below with reference to FIGS. 3 to
5.
[0032] FIG. 3 is a schematic view showing the external appearance
of the projection display 1; FIG. 4 is a side view, seen from the
direction indicated by an arrow A1, showing the projection display
1 of FIG. 3; and FIG. 5 shows one example of the internal structure
of the projection display 1. In addition, FIG. 6 diagrammatically
shows an optical system of FIG. 5.
[0033] As shown in FIGS. 3 and 4, the projection display 1 includes
a main body 11, a projection lens barrel 13, a PS conversion unit
15 and the light source 3.
[0034] The main body 11 is integrated with the projection lens
barrel 13 which includes, as shown in FIG. 5, a projection lens
group 17 having various kinds of lenses 17a to 17i. The projection
lens barrel 13 has a mechanism capable of focusing the projection
light rays (image light rays) 5 on the backface 104 of the screen
102 shown in FIGS. 1 and 2.
[0035] The main body 11 removably holds the PS conversion unit 15,
and has the following components. A first fly eye lens 21 and a
second fly eye lens 23 are disposed near the PS conversion unit 15
in such a manner as to be spaced from and in parallel to each
other. Along an optical axis OP from the second fly eye lens 23 to
the projection lens group 17 are arranged the following optical
elements. That is, dichroic mirrors 25 and 27, a relay lens 29, a
mirror 31, a relay lens 33, and a mirror 35 are arranged in this
order from the second fly eye lens 23.
[0036] Another mirror 37 is arranged, near the dichroic mirror 25,
along an optical axis OP1 perpendicular to the optical axis OP. In
a region surrounded by the dichroic mirror 27 and mirrors 35 and 37
is arranged a dichroic cube 41. A liquid crystal display (LCD:
image display element) 45 for blue (B) is arranged between the
dichromic cube 41 and a condenser lens 43; a liquid crystal display
(LCD: image display element) 49 for green (G) is arranged between
the dichroic cube 41 and a condenser lens 47; and a liquid crystal
display (LCD: image display element) 53 for red (R) is arranged
between the dichroic cube 41 and a condenser lens 51. The dichroic
mirror allows light in a specific wavelength region to pass
therethrough and allows light in the remaining wavelength region to
be reflected therefrom.
[0037] As shown in FIGS. 4 to 6, the light source 3 is mounted on
the main body 11, and as shown in FIG. 5, the light source 3 has a
reflector 55 and a lamp 57 represented by a metal halide lamp.
Light rays L generated by the lamp 57 are reflected from the
reflector 55 having a parabolic plane to be formed into
substantially parallel light rays LP which are fed to the PS
conversion unit 15 side.
[0038] The PS conversion unit 15 will be described with reference
to FIGS. 6 to 9.
[0039] The PS conversion unit 15 functions as a PS polarizing
device for receiving the parallel light rays LP formed by the
reflector 55 of the light source 3 and deriving therefrom, for
example, only a S wave (S polarized light component: first
polarized light component) as shown in FIG. 8. The parallel light
rays LP contain a P wave (P polarized light component: second
polarized light component) and the S wave (first polarized light
component). When the P and S waves pass through the PS conversion
unit 15, only one wave, for example, the S wave is derived by the
PS conversion unit 15. The S wave is then fed to the first fly eye
lens 21 side shown in FIG. 5.
[0040] The PS conversion unit 15 has, as shown in FIGS. 7 and 8, a
case 61, two sheet-type polarized light separating mirrors 63
(first sheet-type polarized light separating mirror and second
sheet-type polarized light separating mirror), two quarter-wave
plate mirrors 65, and one half-wave plate 67.
[0041] The two polarized light separating mirrors 63 are arranged
such that the plane of each mirror is tilted at a specific angle
.theta. with respect to the optical axis OP2 of FIG. 5, as seen
from the direction indicated by an arrow A2, that is, seen in the
direction parallel to the optical axis OP2 of the projection lens
barrel 13 shown in FIGS. 5 and 6. That is to say, the two polarized
light separating mirrors 63 are arranged symmetrically with respect
to the optical axis OP with each of the planes thereof tilted at an
angle .theta. with respect to the optical axis OP. The angle
.theta. is preferably set in a range of 10 to 30.degree., more
preferably, at an approximately 20.degree..
[0042] If the angle .theta. of the polarized light separating
mirror 63 becomes smaller from 10.degree., the transmittance for
the S wave of the polarized light separating mirror 63 shown in
FIG. 8 becomes smaller and the necessary transmitted amount of the
P wave becomes smaller. This is undesirable because it is difficult
to sufficiently separate the P and S waves from each other.
[0043] If the angle .theta. becomes larger from 30.degree., the
transmittance for the S wave becomes larger, and the transmitted
amount of the P wave becomes smaller. This is undesirable because
it is difficult to sufficiently separate the P and S waves from
each other.
[0044] The half-wave plate 67 is mounted to the leading ends, which
are opened, of the polarized light separating mirrors 63 in such a
manner as to be perpendicular to the optical axis OP.
[0045] The PS conversion unit 15 shown in FIG. 8 derives a desired
wave, for example, S wave from the parallel light rays LP
(containing the P and S waves), that is, polarization-converts only
one of the separated light components. In the example shown in FIG.
8, when the substantially parallel light rays LP enter the two
polarized light separating mirrors 63 (incident angle:
90.degree.-.theta., for example 70.degree.), the P wave passes
through the polarized light separating mirrors 63, but the S wave
is reflected from the polarized light separating mirrors 63 and
reaches the quarter-wave plate mirrors 65. The S wave is reflected
from the quarter-wave plate mirrors 65 and fed in parallel to the
optical axis OP. On the other hand, the P wave, which has passed
through the polarized light separating mirrors 63, is
polarization-converted into the S wave by the half-wave plate 67
and is fed as the S wave in parallel to the optical axis OP.
[0046] In this way, only the S wave is polarization-separated from
the parallel light rays LP and is fed to the subsequent first fly
eye lens 21 side. In this example, since only the S wave is used by
removal of the unnecessary polarized light component (P wave), a
heat load applied to the incident side polarized sheet from the
light rays generated by the light source 3 can be reduced, and the
illumination efficiency of the S wave can be also increased. That
is to say, even if the light quality of the lamp of the light
source 3 is doubled, it is possible to suppress at low values
temperatures of the polarized light separating mirrors 63,
quarter-wave plate mirrors 65, half-wave plate 67, and the
subsequent elements disposed from the fly eye lens to the
projection lens system.
[0047] Each polarized light separating mirror 63 is preferably
coated with a single TiO.sub.2 film. With this configuration, the
polarized light separating mirror 63 can be prepared at a cost
lower than that of a prism type polarized light separating element,
and also the incident angle (90.degree.-.theta.) can be set at a
large value, for example, about 70.degree..
[0048] The first and second fly eye lenses 21 and 22 as an optical
integrator shown in FIG. 5 will be described.
[0049] FIG. 11 shows the first fly eye lens 21 and FIG. 12 shows
the second fly eye lens 23. The first fly eye lens 21 is formed by
collecting on a plane a number of rectangular lenses 21a. The
second fly eye lens 23 is formed by collecting on a plane four
large-sized central lenses 23a and various peripheral lenses 23b,
23c, 24d and 23e each being different in size from the lens 23a.
The first and second fly eye lenses 21 and 23 are disposed behind
the PS conversion unit 15 shown in FIG. 5 for equalizing the
intensity distribution of, for example, S wave formed by the PS
conversion unit 15. The equalized light rays are then fed to the
dichroic mirror 5 and the later shown in FIG. 5.
[0050] In the second fly eye lens 23, each of the four lenses 23a
located at the central portion is set to be larger than each of the
peripheral lenses for the purpose of most efficiently receiving the
lamp arc image from the light source 3. Preferably, the central
portion is divided into four parts on which the four large-sized
lenses 23a are located. In the case where the incident angle of the
parallel light rays LP from the light source 3 is large (for
example, x2 shown in FIG. 12), that is, the size of the
image-formation of the parallel light rays LP is large at the
central portion of the second eye lens 23, the large-sized lenses
23 are allowed to receive such light rays LP. On the contrary,
since the incident angle of the parallel light rays LP is
relatively small at the periphery portion of the second fly eye
lens 23, the small-sized lenses 23c, 23d and 23e for example are
located at the peripheral portion.
[0051] FIG. 13 shows another example of each of the first and
second fly eye lenses 21 and 23 shown in FIGS. 11 and 12. As shown
in this example, each of the fly eye lenses 21 and 23 may be
replaced with a fly eye lens 121 having lenses 121a which are equal
in size to each other.
[0052] FIG. 10 shows changes in transmittance (for the P wave or S
wave) of each sheet-type polarized light separating mirror 63 of
the PS conversion unit 15 with the wavelength of the parallel light
rays LP obtained by the lamp of the light source 3 taken as a
parameter. In this case, as shown in FIG. 9, the incident angle of
the P and S waves is set at (90.degree.-.theta.). From the
separation characteristic of the polarized separating mirror 63
shown in FIG. 10, it becomes apparent that the tilting angle
.theta. of the plane of the polarized light separating mirror 63
with respect to the optical axis OP is desired to be set, as
described above, in a range of 10 to 30.degree.. It is to be noted
that the polarized light separating mirror exhibiting the above
separation characteristic is preferably coated with the TiO.sub.2
film.
[0053] Next, an example of operating the projection display 1
housed in the above-described television set will be described.
[0054] Referring first to FIG. 5, the lamp 57 of the light source 3
generates light rays which are formed into substantially parallel
light rays LP. The parallel light rays LP enter the polarized light
separating mirrors 63 of the PS conversion unit 15 shown in FIG. 8.
At this time, the P wave contained in the parallel light rays LP
passes through the polarized light separating mirrors 63 but the S
wave is reflected from the polarized light separating mirrors 63,
reaching the quarter-wave plate mirrors 65, and is reflected
therefrom to be introduced as the S wave in parallel to the optical
axis OP.
[0055] On the contrary, the P wave, which has passed through the
polarized light separating mirrors 63, passes through the half-wave
plate 67 to be converted into the S wave.
[0056] Accordingly, the PS conversion unit 15 functioning as the PS
convertor derives only the S wave from the parallel light rays LP
(containing the P and S waves) and removes the P wave as the
unnecessary polarized light component. As a result, even if the
light quality of the light source 3 is larger, the heat quality
thereof can be reduced, so that it is possible to suppress at
relatively low values temperatures of the polarized light
separating mirrors 63 and the optical elements subsequent thereto,
and to increase the illumination efficiency of the S wave.
[0057] Since each of the polarized light separating mirrors 63 is
tilted at a relatively small angle .theta. with respect to the
optical axis OP as shown in FIG. 8, the size of the case 61 of the
PS conversion unit 15 shown in FIG. 7 can be reduced, and since the
sheet-type polarized light separating mirror 63 is very lower in
cost than the prism type polarized light separating element, the
total cost can be reduced.
[0058] The S wave obtained as shown in FIG. 8 passes through the
first and second fly eye lenses 21 and 23 to be equalized and
reaches the dichroic mirror 25 shown in FIG. 5. Then, part of the
light rays (S wave) are introduced to the dichroic mirror 27 and
the remaining one are introduced to the common mirror 37.
[0059] The light rays reflected from the mirror 37 pass through the
condenser lens 51 and reaches the liquid crystal display 53 for red
(R). An image displayed on the liquid crystal display 53, which is
projected by the light rays from the mirror 37, is reflected from a
semi-transparent film 41a of the dichroic cube 41 and is introduced
to the projection lens group 17.
[0060] Part of the light rays reaching the dichroic mirror 27 is
fed to the relay lens 29 and the rest reach the liquid crystal
display 49 for green (G) through the condenser lens 47. An image
displayed on the liquid crystal display 49 is projected by the
light rays, passing through the semi-transparent film 41a of the
dichroic cube 41, and is introduced to the projection lens group
17.
[0061] The light rays, which have passed through the relay lens 29,
are reflected from the mirror 31, passing through the relay lens
33, and are reflected again from the mirror 35 along the optical
axis OP3. The light rays are thus bent substantially 180.degree.
from the optical axis OP to the optical axis OP3, and are
introduced to the liquid crystal display 45 for blue (B) through
the condenser lens 43. An image displayed on the liquid crystal
display 45 is projected by the light rays, being reflected from a
semi-transparent film 41b of the dichroic cube 41, and is
introduced to the projection lens group 17.
[0062] The images of R, G and B are then superimposed to each other
through the projection lens group 17, to form light rays 5 to be
projected. The light rays 5 are reflected from the mirror 103 shown
in FIG. 2, and are projected on the backface 104 of the screen 102.
The projected color image can be viewed from the front side of the
screen 102 by the user U.
[0063] Other embodiments of the present invention will be described
below.
[0064] FIG. 15 shows another embodiment of the projection display
of the present invention. A projection display 101 is different
only in structure of a PS conversion unit 115 from the projection
display 1 shown in FIG. 8, and therefore, the description of the
basic configuration is omitted.
[0065] The PS conversion unit 115 of the projection display 101
shown in FIG. 15 has two sheet-type polarized light separating
mirrors 163, two quarter-wave mirrors 165 and two half-wave plates
167. Like the embodiment shown in FIG. 8, the polarized light
separating mirrors 163 are symmetrically disposed with respect to
the optical axis OP such that the plane of each mirror is tilted at
an angle .theta. with respect to the optical axis OP, and the
quarter-wave plate mirrors 165 are disposed substantially in
parallel to the polarized light separating mirrors 163. On the
other hand, differently from the embodiment shown in FIG. 8, each
half-wave plate 167 is mounted between the polarized light
separating mirror 163 and the quarter-wave plate mirror 165.
[0066] When the substantially parallel light rays LP generated by
the light source 3 enter the polarized light separating mirrors
163, the p wave passes through the polarized light separating
mirrors 163, but the S wave is reflected therefrom and reaches the
quarter-wave plate mirrors 165. The S wave is reflected from the
quarter-wave plate mirrors 165, and is then converted into the P
wave by the half-wave plates 167. That is to say, the PS conversion
unit 115 can derive only the P wave from the parallel light rays LP
by polarization-converting the S wave. Even in the case of using
the P wave, like the embodiment shown in FIG. 8, the heat quality
applied to the polarized light separating mirrors 163 of the PS
conversion unit 115 can be reduced to about half, to suppress
temperatures of the optical elements at low values and to increase
the optical efficiency of the polarized light component used.
[0067] In this case, from the reason described in the embodiment
shown in FIG. 8, the angle .theta. is preferably set in a range of
10 to 30.degree., more preferably at 20.degree.. In addition, the
polarized light separating mirrors 163 are arranged in the
direction (normal to the paper plane of FIG. 15) perpendicular to
the optical axis OP2 of the projection lens group 17.
[0068] FIG. 16 shows a further embodiment in which the PS
conversion unit 115 is positioned between the first and second fly
eye lenses 21 and 23. FIG. 17 shows still a further embodiment in
which the PS conversion unit 115 is positioned behind the second
fly eye lens 23.
[0069] The arrangement examples shown in FIGS. 16 and 17 can be
applied to the PS conversion unit 15 shown in FIG. 8.
[0070] FIG. 14 shows a projection display 201 as an additional
embodiment in which a liquid crystal display 249 is arranged
between a dichroic cube 241 and a condenser lens 247. The liquid
crystal display 249 is an image display element for simultaneously
projecting images of three-primary colors (R, G, B).
[0071] With this arrangement, the number of the components of the
optical system can be significantly reduced. Also the projection
display 201 using one liquid crystal display 249 can be used for
monochromatic display.
[0072] The present invention is not limited to the above
embodiments.
[0073] While the kind of the liquid crystal display is not
particularly limited in the above embodiments, the liquid crystal
display may be represented, for example, by a liquid crystal
display panel using a polycrystalline Si-TFT (thin film
transistor). Also the TiO.sub.2 film formed on the polarized light
separating mirror 63 shown in FIG. 8 or the like may be replaced
with other films made from, for example, ZrO.sub.2,
Ta.sub.2O.sub.5, and a material having a refractive index
nd.gtoreq.2.0.
[0074] While the liquid crystal display is used as the image
display element in the embodiments, the present invention can be
applied to other display elements such as a reflection type liquid
crystal display.
[0075] The light source is not limited to the type using a metal
halide lamp. For example, other light sources such as a halogen
lamp, mercury lamp and xenon lamp can be adopted.
[0076] The projection display of the present invention can be
applied not only to the type in which an image is projected on the
backface of the screen shown in FIG. 1 but also to the type in
which an image is directly projected on the front face of the
screen.
[0077] While a television set is used as the system to which the
projection display is applied in the embodiments, the present
invention can be applied to other monitors.
* * * * *